The present invention relates to a gas circulating method and apparatus for an autoclave which is used to heat and compress such moldable materials as multilayered structures made of fiber reinforced plastics (FRP) used as parts of aircraft and industrial machines, and tools etc., and moldable elements such as multilayered print wiring circuit boards used as parts of electronic devices.
Hitherto, many techniques which heat and compress the moldeble materials of FRP or print wiring, circuit boards within an autoclave to mold them are known from such publication as Japanese laid-open patent publications Nos. 58-62018, 60-258996, 61-94742, and 62-28228 for example.
As shown in FIGS. 5, 6 and 7, these techniques comprises: a pressure container A having a wind tunnel 7, in which moldable materials 1 are placed and gasses are circulated by a blower fan 33, the container A being sealably closed by a door 2; compressing means B for supplying high pressure gasses into the pressure container to compress the moldable materials 1; means C for heating and cooling the high pressure gasses contained in the container with a heat exchanger 5 settled rearwardly in the inside of the pressure container; a fan driving unit E including a motor 30 which is located outside of the pressure container and carriers the fan 33 in the container, passing through a sealing unit 34, the fan 33 being driven to circulate the gasses heated or cooled by the heating and cooling means into the inside 7b of wind tunnel 7 through its outer duct 7a; and means D for highly depressuring the inside of a vacuum bag 12 containing the moldable materials 1 and closed up tightly.
Furthermore, as shown in FIGS. 5 and 6, the moldable materials 1 are placed on a jig., or mold 9 of a bed 11, covered with a breather cloth and the vacuum bag 12 in turn, and sealed closed by sealant (made of silicone sealing agent). The enclosed materials 1 are then brought into the pressure container A, and the external depressurizing means D is communicated with the inside of the vacuum bag 12 so as to depressurize it after the pressure container is sealed. After the inside of the vacuum bag 12 is depressurized, a high pressure gas (inert gas) is supplied in the pressure container A and heated therein so as to compress the moldable materials 1. The heated high pressure gas is, for circulation, driven by the fan 33 to flow through the outer duct 7a of the wind tunnel 7, and be diverted by the door's inner wall face 2a into the inside 7b of the wind tunnel, whereby the layers of the moldable materials 1 are compressed and heated to be molded, stiffened and bound together.
Those techniques, however, have such problems as described below.
The gas which is driven by the fan 33 to flow through the outer duct 7a formed between the inner wall Aa of the container and the wind tunnel wall 6, and to the diverted by the inner wall face 2a of the door has large cavities 10a (air pockets) extending over the range between the distal end of the outer duct 7a and the inside 7b of the wind tunnel, as shown in FIG. 5. Therefore, the distribution of the velocity of the wind is disoriented to spread the distribution of the temperature of the gas in a disordered manner. Further, the gas flowing through the inside 7b of the wind tunnel tends to coverge at the center of the inside 7b of the wind tunnel, whereby the distribution 35 of the velocity of the wind shown in FIG. 7 is obtained.
As a result, the moldable materials 1 respectively placed near the entrance of the pressure container A and near the inner periphery of the inside 7b of the wind tunnel are not heated equally, and in addition the materials 1 put under the wind having such distribution of the velocity do not receive enough wind on the downstream side 14 shown in FIG. 5, whereby the materials 1 are unequally heated on the different portions thereof which receive or do not receive the wind. Thus, the products finished through the stiffening and adhering have problems in their quality due to the unequal heating. Consequently, the products having the unequally adhered layers can not be used as parts and structures of spacecraft devices aircraft, etc. which attach great importance to the reliability of the parts.
Therefore, the entrance area of the pressure container A and the peripheral area of the inside 7b of the wind tunnel can not be reliably used. Moreover, the spaces between materials 1 placed on the bed need to be broadened so as to avoid the unequal heating on the downstream sides 14 of the materials 1, which results in substantially preventing the effective use of the autoclave.